Rotary converter.



L. W. CHUBB.

ROTARY CONVERTER.

APPLICATXON FILED AUG3. 1917.

Patented Mar. 5, 1918.

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' UNITED STATES PATENT OFFICE.

LEWIS W. CHUBB, 0F PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSEELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

ROTARY CONVERTER.

Patented Mar. 5, 1918.

Original application filed July 6, 1915, Serial No. 38.120. Divided andthis application filed August: 3, 1917.

Serial No. 184,246.

To all whom it may concern.

Be it known that 1, Lewis V. CIIUBB, a citizen of the lnited States, anda. resident of Pittsburgh, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement in RotaryConverters, of which the following is a specification, this applicationbeing a division of application Serial No. 38,120, filed July 6,1915.

My invention relates to rotary converters and to auxiliary apparatus tobe employed in conjunction therewith, and it has for its object toprovide apparatus of the character designated whereby armature h atingmay be reduced and such heat as is produced may effectively bedistributed, thus permitting an increase in the load rating of a givenrotary converter.

In the accompanying drawing, Figure 1 is a diagrammatic view of a rotaryconverter arranged in accordance with my invention; Fig. 2 is a diagramillustrating the distribution of heat in the different armature coils ofa rotary converter operating in accord ance with my invention, ascontrasted with an ordinary rotary conyerter, and Fig. 3 is a diagramillustrating the method in which more efl'ective current cancellationmay be obtained.

In the ordinary rotary converter, it is well known that the heating ofan armature conductor in a machine of given capacity is far less than ina corresponding direct-current machine because of the fact that anygiven armature coil tends to be simultaneously traversed by analternating-current sine wave of supply current and by a squaredop,direct-current wave of load current of opposite phase, the heating beingproduced by the resultant current How. It is further well known that, inaccordance with Fouriefs series, any periodically recurring wave may beresolved into the sum of a series of pure sine waves of multiplefrequencies. Thus, the square-top Wave of direct current tending to flowin a given armature conductor may be resolved into the sum of a slneWave of the frequency of the supply, of a sine Wave of three times saidfrequency, of five times said frequency, etc. In the ordinary convcrter,said fundamental component of the square-top Wave is substantially equaland opposite to the alternating-current supply wave, the residualcurrent 1n the armature conductor being the difference between thesefundamental components and the sum, to infinity, oi the highenfrequencycomponents. By supplying circulating current to the armature winding ofthree times the primary frequency and of such phase and magnitude thatthe third harmonic component of the squarctop wave issubstantiallyneutralized, a further 'adical reduction in the heating maybe secured, the ctlect of the sum, to infinity, of the fifth and higherharmonic components of the square-top wave being negligible. Inaccordance with my invention, I provide means whereby athird-harmonie-current component satisfying the above-named conditiionsmay be produced and supplied, par ticularly in a twelve-phase converter.

Referring to the drawing for a more detailed umlerstanding of myinvention, I show a rotary converter diagrammatically in Fig. i. saidconverter comprising an .armature t and a field-pole structure indicateddiagraimnatically at 5-5. The armature 4 is provided with a winding 6 ofusual type, 'said winding being appropriately adapted for connection toa. twelve-phase source of alternating current 7 by means of suitableleads S--S. Direct current is derived irom the winding (3 by acommntating device of any well known structure, said commutating devicebeing indicated by brushes 9-9 bearing directly upon the winding 6.

Means are provided for developing a sine component of current of threetimes the frequency of the source 7 in at least two of the leads 8 ofthe winding 6. Said means is indicated diagrammatically at 10 and maycomprise an auxiliary synchronous dynamoclectric machine having suchpole number and driven at such speed and phase as to supply current ofthe desired character. Said sine component of triple frequency may alsobe developed within the rotary converter itself by suitable modificationof the machine constants, as is well known in the art.

Having thus described the arrangement of a machine embodying myinvention, attention is directed to Fig. 3 for an understanding of theoperation thereof. The direct-load current of the rotary converter istransformed by the action'of the commutater into a series of'square-top-current wares within the armature current, two of said Wavesbeing indicated at 13, 14:, 15, 16, 17, 18 and 19. Thealternating-current supply tends to produce a sine wave of current inthe same mid coil. of the armature, 180 out of phase with saidsquare-top Waves, as indicated at 13, 20, 16, 21, 19. The squaretop Wave131ei-l5-16 may be resolved into a fundamental sine Wave 13-27 1628-19,a triple-frequency component 13-2916-3019 and a residual Wave131l31-1516l7 32-1819, said residual wave representing the sum, toinfinity, of the fifth and highercomponents of the square-top wave. Thefundamental component 132716 substantially cancels thealternating-current-supply wave 13-20-16 and, by the action of thetriple frequency source 10, I tend to develop a triple-fie quencycurrent l83516 that is equal andopposite to the triple-frequencycomponent l3-2916, thus neutralizing said triplefrequency component andeliminating its heating action. As a result, there is left only theresidual wave 131 l-31-15-16.

Referring to Fig. 2, the curve 11 represents the percentage of theheating in the equivalent direct-current machine for armature coilshaving different angular displacements from the mid coil in the ordinarytwelve-phase converter, and the curve 12 correspondingly indicates thepercentage of direct-current heating for the corresponding armaturecoils in a rotary converter embodying my invention. it will be notedthat there is a reduction in'the heating of all of the coils but thatthe percentage reduction in the mid coil s considerably greater thanthat of the tap coils.

While I shouzn my invention in its preferred rm, it'will be obvious tothose skilled in the that it is susceptible of various minor changes andmodifications without departing from the spirit thereof and I desire,therefore that only such limitations shall be placed thereupon as areins-- posed by the prior art or as are specifically set forth in theappended claims.

I claim as my invention:

1. The combination with a twelve-phase rotary converter, of means forcirculating substantially a sine component of current of triplefrequency through the armature winding thereof.

2. The combination with a twelve-phase rotary converter, .of a mainsource of alternating current connected thereto and an auxiliarydynamo-electric machine arranged to supply a sine component of currentof three times the frequency of said source to at least two phases ofsaid converter.

3. The combination With a twelve-phase rotary converter, of a source ofalternating current and a load circuit connected thereto,

whereby alternating-current waves and square-top direct-current Waveshaving a relative phase displacement of substantially 180 flow in thearmature winding thereof,

and means for supplying current to said winding of such frequency, phaseand magnitude as to substantially neutralize the third harmoniccomponent of said square-top Wave.

4. The combination with a twelve-phase rotary converter, of a source ofalternating current and a load circuit conected thereto, wherebyalternatingcurrent Waves and square-top direct-current Waves having arelative phase displacement of substantially 180 tend to iiovv in thearmature winding thereof, and an auxiliary dynamo-electr1c machinearranged to supply current to said winding of such frequency phase andmagnitude as to substantially neutralize the third harmonic component ofsaid square-top wave.

5. The method of reducing armature heat ing in a twelve-phase rotaryconverter which comprises circulating a sine component of current ofthree times the supply frequency through a portion of the armaturewinding thereof.

Intestiinony whereof, I have hereunto subscribed my name this 18th dayof July, 1917.

LEWIS W. CHUEB.

